1. Field of Invention
The present invention is directed to a method for manufacturing a honeycomb structure having slits and having a plurality of rays of numerous cells aligned in parallel, an apparatus for manufacturing the same, and more particularly to a method for manufacturing a honeycomb structure having slits formed along arrays of numerous cells aligned in parallel and communicating with an external space, and an apparatus for manufacturing the same.
2. Related Art Statement
A honeycomb structure is known as a structure in which a plurality of arrays of numerous cells are formed by being aligned in parallel to a base, and is used as a light yet strong structural member for aircraft or the like, and a catalyst carrier having a large air flow for automotive exhaust gas purification or the like. Additionally, it is utilized as a dust filter or a solid-liquid separation filter having a large filtering area per unit volume, in a case where the base is made of a ceramic porous material having fine pores.
The aforementioned applications are derived from the feature of the honeycomb structure in that it has a plurality of cells isolated from external space, however, slits communicating with external space are formed on the structure by deliberately cutting or grinding parts of the cells for certain purposes.
For instance, a honeycomb structure 21 shown in FIG. 2(b) is a solid-liquid separation filter for removing insoluble matters of a particle diameter larger than the pores of a base 22 by injecting a liquid to be treated into cells 23 and by letting only a filtrate that has passed the pores of the base 22 flow out to external space. A part of the cells 23 is deliberately cut or ground along the specific cell arrays 26a out of a plurality of cell arrays 26 to form slits 24, thereby the structure can communicate with external space. Such a honeycomb structure will be referred to hereinafter as a honeycomb structure having slits.
In such a solid-liquid separation filter, as a filtrate having passed the inside of the base 22, i.e. cells near the central part, flows out directly through the slits 24 to external space, the traveling distance of the filtrate through pores of the base 22 can be shortened to reduce the fluid resistance during filtration. This results in the advantage that, even where a filter having a large volume is used, the liquid throughput is not reduced and a sufficient filtering capacity can be retained.
Furthermore, the contamination of the filtrate with a liquid to be treated can be prevented merely by sealing the cell arrays 26a in which the slits 24 are formed at the both ends of said arrays 26a with a sealing member 25 made of glass or the like.
According to the conventional methods, a honeycomb structure having slits as described above is manufactured by drying and firing ceramic body after extruding and:
(1) marking off the external side face of the structure in such a manner that the specified cell arrays in which slits are to be formed at both end faces of the honeycomb structure where cell openings are located, are connected with the marked off line, and forming the slits by cutting or grinding the marked off portions with a micro-grinder, drill or the like. This method is hereinafter referred to as a first method; or
(2) forming slits by cutting the structure along the specified cell arrays with a grind stone or the like watching with naked eyes to determine the position of the cell arrays of the honeycomb structure at which the slits are to be formed. This method is hereinafter referred to as a second method.
However, in the case of the first method, it is not possible to eliminate machining errors such as breaking arrays of adjacent cells or cutting cell walls of adjacent cells, even cuffing the marked off portions accurately. This is because it is not so easy even for well-experienced workers to cut or grind the targeted cell arrays alone, in addition to the troublesome manual work of marking off. This is because the cell arrays in which slits are to be formed are not always positioned along the lines connecting the cell arrays marked off at the end faces where cell openings are located of the structure due to the frequent distortion and/or frequent deformation of cell arrays, which is derived from the compression or the deformation of the molded article during the steps of extruding, drying and firing the molded article.
That is, the first method is not a simple one fitted for mass production, and furthermore it is difficult to form fine slits accurately.
The difficulty in forming fine slits accurately means that the formation of slits in a honeycomb body of such a fine structure that one having fine cell pores of 2 to 3 mm and having a wall thickness of about 0.5 mm is extremely difficult.
The second method, on the other hand, can reduce machining errors because slits are formed while watching the cell arrays with naked eyes, compared with the first method. However, there is still a problem since it requires such troublesome manual work that one should cut into the end faces of the structure while watching the cell arrays with naked eyes. Accordingly, one may say that fine slits can be formed accurately by utilizing the second method, however, there is a problem in that it is not simple to apply it to mass production.
Moreover, there is another problem in the second method in that the mechanical strength at the two ends of the structure is weakened because, inevitably, slits are formed there. The weakened mechanical strength at the two ends of the structure is not preferable. This is because the filter is easily broken by mechanical forces such as distortion or impact given thereto at the time of fitting; and the bending stress derived from the dimensional tolerance of the structure or the surface pressure of sealing, in the case that one uses the structure as a solid-liquid separation filter by utilizing both ends of the structure as a sealing portion at the time of fixing it at both ends.
Moreover, the formation of the slits is no an easy task in either the first method and the second method since a honeycomb structure hardened and densified after firing should be used for the processing of the slits in both methods. The second method may be applied to a molded article before drying and firing, however, it is not preferable since there is a fear of magnifying the contraction or deformation of the structure at the two ends at the time of drying and firing. This might cause sealing failure when the structure is used as a solid-liquid separation filter.
As hitherto described, any conventional method for manufacturing a honeycomb structure having slits is not satisfactory since it is furnished with neither formation of slits in accuracy and fineness nor sufficient simplicity fitted for mass production.
The present invention has been made so as to solve those problems. That is, the object of the present invention is to provide a method for manufacturing a honeycomb structure having slits capable of forming accurately fine slits by cutting or grinding the specified cell arrays alone, and being fitted to mass production.
The present invention has been completed, as a result of intensive studies, based on the findings that those problems mentioned above can be solved by adopting a slit forming method in which a slit forming member is protruded during the step of extruding a honeycomb structure.
Thus, according to the present invention, there is provided a method for manufacturing a honeycomb structure having slits and having a plurality of arrays of numerous cells aligned in parallel; the slits communicating with external space and being formed along the cell arrays, wherein the slits are formed during the step of extruding a honeycomb structure by protruding a slit forming member toward the molded article during that time.
In the method according to the present invention, slits can be formed during the extrusion step with the formation of cells, or alternatively the slits may be formed by cutting the specified arrays after the formation of the cells.
Further in the method according to the present invention, it is preferable to monitor the position of the molded article during the step of the extrusion, and to control the actions of the slit forming member based on the monitoring.
Further according to the present invention, there is provided an apparatus for manufacturing a honeycomb structure having slits and a plurality of arrays of numerous cells aligned in parallel; the slits communicating with external space and being formed along the cell arrays, which comprises an extruder having an extruding die for a honeycomb structure, and a slit forming member installed near the extruding die and capable of protruding along specified cell arrays of a molded article being extruded in which slits are to be formed.
In the apparatus according to the present invention, the slit forming member may be arranged so as to protrude either inwardly or outwardly toward the extruding die. Where the slit forming member is arranged so as to protrude outwardly the extruding die, a J-shaped bit is preferable as a slit forming member.
Further, it is preferable to have monitoring means for monitoring the position of the molded article being extruded and control means for controlling the actions of the slit forming member based on the monitoring data.